All For One renames the boy Tomura Shigaraki , with "Tomura" signifying "to mourn" and "Shigaraki" being All For One's own surname, marking him as his official successor. The Battle in Deika City
The massive beast Gigantomachia arrives on the scene, finally acknowledging Shigaraki as a worthy successor to All For One. Formation of the Paranormal Liberation Front Boku no Hero Academia 5th Season (Dub) Episode 24
The episode ends with a significant shift in the series' power balance: Boku no Hero Academia Season 5 - Episode 24 discussion All For One renames the boy Tomura Shigaraki
As his memories return, Shigaraki's "Decay" quirk undergoes a massive awakening. He is now able to spread decay through physical contact with the ground, effectively leveling entire city blocks with a single touch. Boku no Hero Academia 5th Season (Dub) Episode 24